emulsions (lecture 4)

Question 1

Pharmaceutical emulsions

Answer 1

• Pharmaceutical emulsions can be administered by mouth, injection (e.g. IV), and topically on the skin (e.g. lotions, creams, ointments).

Question 2

Dispersed phases

Answer 2

• Dispersed phases of oil (o) and water (w) stabilized together in the presence of emulsifiers

Course emulsions or colloidal dispersions (i.e. microemulsions/nanoemulsions).

Question 3

Dispersions

Answer 3

with an internal phase and an external phase creating an interface

Question 4

External phase

Answer 4

is the bulk phase also called the continuous phase

Question 5

nternal phase

Answer 5

are the droplets that are suspended and is called the dispersed phase

Question 6

Coalescence (flocculation)

Answer 6

leads creation of flocs (clumps as larger droplets) and then break down (cracking) leading to phase separation and then creaming of the emulsion which is thermodynamically favorable, since it reduces the interfacial energy

Question 7

Kinetic stability with thermodynamic instability

Answer 7

Ø Controlled flocculation
Ø Shake well before use
Ø Properly store
Ø Preservatives needed for long shelf-life to prevent microbial growth which will cause flocculation and cracking (e.g. spoiled milk)
Ø Compounded emulsions have shorter shelf-life than manufactured emulsions

Question 8

• Single emulsion types:

Answer 8

o/w or w/o

Question 9

• Double emulsion types

Answer 9

• Double emulsion types: o/w/o or w/o/w

Question 10

• Nanoemulsio

Answer 10

• Nanoemulsion type: o/w

Question 11

Viscosity modifiers

Answer 11

§ Viscosity modifiers can promote physical stability by slowing down coalescence through “thickening” e.g. egg yolk, acacia, agar, pectin, gelatin

Question 12

emulsifier provides…

Answer 12

§ The emulsifier provides a film barrier that protects the droplets from coalescing together by either steric hindrance leading to steric repulsion or electrostatic effects leading to electrostatic repulsion.

Question 13

Emulsifiers

Answer 13

§ Emulsifiers: are surfactants forming a film barrier at the internal/external phase interface, can be natural (e.g. egg yolk, acacia, agar, pectin, gelatin) or synthetic (e.g. nonionic surfactants, cationic surfactants, anionic surfactants, fatty acids, or synthetic polymer)

Question 14

Emulsifiers reduce the interfacial energy at the interface to provide physical stability

Answer 14

Ø Film is typically a monomolecular layer (monolayer) at the interface Ø Nonionic surfactants act through steric repulsion
Ø Synthetic nonionic polymers act through steric repulsion
Ø Cationic and anionic emulsifiers act through electrostatic repulsion

Question 15

HLB (Hydrophilic-Lipophilic Balance)

Answer 15

the HLB (Hydrophilic-Lipophilic Balance) value is the parameter for emulsifiers

Question 16

HLB Range

Answer 16

§ HLB Range =1-20

§ HLB > 10 are more hydrophilic and good for stabilizing o/w emulsions
v High HLB are hydrophilic emulsifiers e.g. Tweens (i.e. polyoxyethylene derivatives of Spans) also known as “polysorbates”
§ HLB < 10 are more hydrophobic and good for stabilizing w/o emulsions
v Low HLB are lipophilic emulsifiers e.g. Spans (i.e. sorbitan esters such as sorbitan oleate) also known as “sorbates

Question 17

different oil emulsions needs different HLBs

Answer 17

Ø vegetable oil emulsions need an emulsifier with HLB=7-8 Ø castor oil emulsions need an emulsifier with HLB=14

§ Can mix different emulsifiers together to get the final HLB value needed